|  | 8.3 | Environmental Factors
| 8.3.4 | Software viruses
All of the previous topics that can affect the performance of a network have dealt with the physical aspect of the network. The last factor that we will talk about that can affect the performance of your network is software. Specifically, a type of software that's sole purpose is to disrupt the operation of a network. Following is a list and description of the different types of infectious software. A Worm is a program that propagates itself across computers, usually by creating copies of itself in each computer's memory. A worm might duplicate itself in one computer so often that it causes the computer to crash. Sometimes written in separate "segments", a worm is introduced unknowingly into a host or network system either for "fun" or with intent to damage or destroy information. The term comes from a science-fiction novel and has generally been superseded by the term virus. A Virus is a program that "infects" computer files (usually other executable programs) by inserting in those files copies of itself. This is usually done in such a manner that the copies will be executed when the file is loaded into memory, allowing them to infect still other files, and so on. Viruses often have damaging side effects, sometimes intentionally, sometimes not. The latest variation is to send these viruses over the Internet as Email attachments. A Trojan Horse is a destructive program disguised as a game, a utility, or an application. When run, a Trojan horse does something devious to the computer system while appearing to do something useful. The previous three paragraphs describe certain types of software that can be damaging to your network or computer. We all try to avoid having things happen to our computers, whether it is physical damage or software damage. Here are some steps that can prevent your network or computers infection by a virus: Be careful about getting software, without knowing specifically where it comes from. Many times software that is distributed through illegal channels is a prime carrier of viruses. This is because there is no system established for checking the software. Be wary of other people using your computer with their disks. Any kind of file can carry a virus. It doesn't have to be a program file; it could just as well be a data file that has a virus infecting it. Use a current virus checker on all computers. There are many companies that sell or provide virus checkers. These are simple things that can be done to protect your computer from viruses. There are many other ways of detecting and preventing viruses that cannot be covered here. If you are worried about viruses, there are many articles and reports that can be obtained through the Internet.
| Web Links
| Computer Knowledge Virus Tutorial
| Current Virus Listings
| Symantec AntiVirus Research Center
| National Institute of Standards and Technology